ARS researchers have modified a method of
producing biobutanol that could make the fuel more competitive with ethanol as
a clean-burning alternative to gasoline. Click the image for more
information about it.

Retooled Approach May Make Bio-based Butanol More
Competitive with Ethanol

A modified method of producing
biobutanol could make the fuel more competitive with ethanol as a clean-burning
alternative to gasoline.

According to Agricultural Research Service (ARS) chemical engineer
Nasib
Qureshi, biobutanol offers several advantages. It can be transported in
existing pipelines, it's less corrosive, it can be mixed with gasoline or used
alone in internal combustion engines, and it packs more energy per gallon than
ethanol.

Until the mid-20th century, biobutanol was produced from fermented sugars
such as corn glucose. But low yields, high recovery costs and petroleum's
increased availability after World War II sidelined fermentation-based systems
for biobutanol production.

Today, petroleum price increases have rekindled interest in tapping butanol
as a biobased fuel, notes Qureshi, with the ARS
National
Center for Agricultural Utilization Research in Peoria, Ill. In 2003, he
began researching the use of wheat straw to make biobutanoldrawn by the
straw's abundance and promise as a lower-cost alternative to corn-glucose-based
feedstocks.

Like other biobutanol processes, his approach employed Clostridium
bacteria to carry out the critical task of fermentation. Such processes
normally involve four preparatory steps (pretreatment, hydrolysis, fermentation
and recovery) carried out separately and sequentially. But Qureshi and
colleagues devised a way to combine three of the four steps. For example,
enzymes and the bacteria are allowed to carry out their respective tasks
simultaneously. Throughout, a procedure known as "gas stripping" is
used to extract the biobutanol as it is produced.

In early trials, the method increased biobutanol productivity by twofold
above traditional glucose-based fermentation. A later adjustment, dubbed
"fed-batch-feeding," increased production even further. For example,
during a 22-day fed-batch operating period, a culture of C. beijerinkcii
P260 converted nearly 430 grams of sugar into 192 combined grams of
acetone, biobutanol and ethanol.

If scaled up further, the process could yield 99 gallons of these three
chemicals from one ton of wheat straw.

Read
more about the research in the October 2008 issue of Agricultural
Research magazine.